Influence by Robert Cialdini - Summary & Notes

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Influence is about six principles of persuasion useful for sales, marketing and negotiation. Professor Robert Cialdini says certain triggers can influence human decisions almost automatically. The six principles are: reciprocity, consistency, social proof, liking, authority and scarcity.

Who is Robert Cialdini?

Dr. Robert Cialdini is one of the world’s top experts on the psychology of influence. His books have sold over 5 million copies in 41 languages. He’s also Professor of Psychology and Marketing at Arizona State University.

Cialdini’s writing relies on a vast amount of scientific research. He also does what could be called investigative research. For this book, he went undercover for 3 years to investigate how the principles of influence are used in the real world by sales organizations, advertisers and fund raisers.

One Goodreads reviewer said this book is “dangerous knowledge” because it shows how people are often misinformed and manipulated. That may be true, but I think it’s better for more people to be aware of these “weapons of influence” than continue living in the dark. (Lucio of ThePowerMoves made a list of other so-called dark psychology books, fascinating stuff.)

So let’s begin with the first lesson from Influence!

1. Automatic Triggers: We are wired to respond predictably to certain cues

In this book, Cialdini will teach us 6 principles of influence. To understand why and how these principles work, we first need to learn that all animals use cognitive shortcuts to make their lives easier.

For example, scientists discovered the nurturing behavior of a mother turkey is triggered almost entirely by the “cheep cheep” sound their baby turkeys make. If the baby doesn’t make the sound, the mother turkey will ignore it.

Surprisingly, scientists could put a tape recorder inside a stuffed cat. If the fake cat also made the “cheep cheep” sound, then the turkey would act nurturing towards it too! Typically, turkeys and cats are natural enemies, but the “cheep cheep” sound triggers an automatic behavior in the turkey that requires no thought.

baby turkey
Cheep cheep?

Well, humans also have similar triggers that are automatic and irrational. Usually they are shortcuts that help us make the right decisions, but sometimes these triggers can be hijacked so we make decisions against our best interests.

For example, adding the single word “because” to a request makes a lot more people say yes to it. A study by Ellen Langer tested how many people would let someone cut into the fron of a line to use a photocopy machine. First they tried asking: “Excuse me, I have five pages. May I use the Xerox machine?” and 60 percent of people said yes. Then they tried asking “Excuse me, I have five pages. May I use the Xerox machine because I have to make some copies?” This time 93 percent of people said yes! The single word “because” caused almost everyone to say yes, even when the reason given was empty!

A well-known principle of human behavior says that when we ask someone to do us a favor we will be more successful if we provide a reason. People simply like to have reasons for what they do.

In Professor Cialdini’s newest book Pre-Suasion, he says before we can influence someone, we first have to get their attention. And the best way to get someone’s attention is through cues related to sex, danger or novelty. He wrote, “Certain cues seize our attention vigorously. Those that do so most powerfully are linked to our survival. Sexual and violent stimuli are prime examples because of their connections to our fundamental motivations to reproduce on the one hand and to avoid harm on the otherβ€”life and death, literally.”

For example, advertisements feature attractive people because we are wired by evolution to be on the lookout for sexual stimuli. The news features violence and natural disasters because we are wired to survive, which means paying close attention to possible danger.

Learn more in our summary of Cialdini’s newest book Pre-Suasion

We sometimes rely on automatic triggers to make decisions. Usually these mental shortcuts help us make the right decisions, but sometimes they can be hijacked. For example, adding the single word “because” to a request caused 33% more people to say yes.

2. Reciprocity: We feel obligated to pay back gifts and favours

In this book, Cialdini will explain six major principles of influence. The first principle is called reciprocity. Reciprocity means we have a natural urge to pay back gifts and favours we have received. In pretty much all human cultures, this is a universal moral rule: Thou shalt reciprocate. People who take without giving tend to be judged negatively and shunned socially.

Professor Dennis Regan at Cornell created a study to test reciprocity. The participants in the study entered a room one-by-one and filled out a questionnaire with a fake participant named Joe, who was really the Professor’s assistant.

For half the participants, Joe stood up in the middle of the experiment and returned with 2 cokes, one for the participant. The other half of the participants didn’t receive this gift from Joe. Later Joe asked them all to buy some raffle tickets from him. And guess what? Those who received the Coke ended up buying TWICE as many raffle tickets as the other group! Yes, people really do pay gifts, even when they are unasked for!

Here are some real life examples of the reciprocity rule in action:

  • Free samples. Businesses give out free samples because they know some people will feel a social obligation to buy the product after the smiling supermarket employee has given them a taste.
  • Small gifts. Charities, hospitals and religious organizations often include a small unrelated gift in their donation requests. The Disabled American Veterans organization doubled the response rate of their mailers (from 18 to 35%) when they included some free labels.
  • Even unwanted gifts work. The Hare Krishna Society gave people on the street a free flower before asking for a contribution. Most people didn’t want the flower, but the volunteers were trained to never take it back. So people felt an obligation to give a dollar or two, before throwing the flower in the nearest garbage bin. With this strategy, they opened hundreds of centers.

The 7 Habits of Highly Effective People may be the best-selling self help book of all time. In it the author Steven Covey shares an idea called “The Emotional Bank Account.” He says we can build deeper and more meaningful relationships if we imagine each one as a separate bank account. That means we should constantly be making new “deposits” into the relationships that are important to us.

For example, if you have kids then you can take them on an adventure, spend time doing what they like or simply listen to them with an open mind. Later on, when conflicts arise in our relationships, then these past deposits will sustain the relationship. (This idea is like the principle of reciprocity applied to social connections. I love it!)

Also check out our summary of The 7 Habits of Highly Effective People

One final point: reciprocal concessions. Cialdini noticed that in negotiations, when one side makes a concession, it is viewed almost like a favour. A concession on one side usually triggers the other side into making their own concession. It’s another form of reciprocity.

This is why savvy negotiators often start with extreme demands. When they make concessions from that starting position, then the other side often feels obligated to make their own (real) concessions. In other words, an effective strategy is to make a big request first, then retreat to a smaller request. The smaller request being what you really wanted in the first place. Cialdini calls this the “Request, then retreat” strategy.

The first principle is Reciprocity, which means we have an urge to pay back gifts and favours. Salespeople, businesses and charities often offer free samples or gifts for this reason. The Disabled American Veterans group found people donated twice as much when they were mailed some free labels.

3. Commitment and Consistency: We want to appear consistent with our past actions

Cialdini’s second principle is Commitment and Consistency. This means we usually want to be consistent with what we have done and said in the past. Unfortunately, this human tendency can lead us down the path of foolish consistency. If someone can make us do a small action, then we’ll be more likely to do larger actions consistent with it in the future.

For example, one study found that if people agreed to put a small 3-inch “Drive carefully” sticker in their home window, then two weeks later they were more than 4 times more likely to agree to put a large sign with the same message in their front lawn! Agreeing with the small request made them feel an obligation to agree to the much larger request two weeks later. This study was done in the 1960s by psychologists Freedman and Frasier.

This principle of consistency is used (consciously or accidentally) in many organizations:

  • Weight loss clinics. People wanting to lose weight are encouraged to write down their goals and share them with everyone. It’s a form of public commitment, and clinics say this often helps their clients stick to the diet when willpower alone would have failed.
  • Door-to-door sales. Companies that sold door-to-door reduced their refunds dramatically simply by having the customer fill out the sales agreement, instead of the salesperson. This act of personally committing to the sale greatly reduced future buyer’s remorse.
  • College fraternities. Why do so many fraternities have embarrassing or painful initiation rituals? Two researchers found the emotionally difficult rituals later caused members to value their membership a lot more. Cialdini wrote:

A pair of young researchers, Elliot Aronson and Judson Mills, decided to test their observation that “persons who go through a great deal of trouble or pain to attain something tend to value it more highly than persons who attain the same thing with a minimum of effort.”

The second principle is Commitment and Consistency. When we make a public commitment, then we feel pressure to appear consistent to it. For example, weight loss clinics tell clients to make their goals public because this helps them stick to the diet.

4. Social Proof: We copy the actions of other people

The third principle is Social Proof. This means we tend to follow what others are doing. If we see many people taking one path, then we assume it’s correct for us to do it too.

For example, when you’re choosing between two similar products on Amazon, are you going to buy the one with 5 good customer reviews or the one with 5000 good reviews? Of course, the one with more reviews. The more people that seem to like a product, the better we assume it is.

In most situations this shortcut helps make our lives easier, but (like the other principles) it can be highjacked. There is a large market for fake online reviews. Companies like Amazon are trying to crack down on this.

Some examples of social proof:

  • Laugh tracks. Many very popular TV shows use fake laughter. If you ask people directly, most of them will tell you they hate laugh tracks. Yet television execs continue to use them because studies show laugh tracks make people rate shows as funnier.
  • Bartenders “salting” tip jars. An empty tip jar at the bar sends the message, “people don’t tip here and that’s okay.” Therefore many bartenders put a few bills into their jar when they start working, which increases their tips because it sends the message that “tipping here is common and expected.”
  • Testimonials. Statements from third parties are obviously more credible than any claims a company makes about its own products. That’s why so many ads showcase the stories of satisfied customers, whether those people are real or made up.

Today we often hear about “influencer marketing.” This is when someone with a large social media audience is paid to promote a product. Like someone who posts a lot about fitness on Instagram could be paid to use a water bottle from a certain brand.

But this is not a new strategy at all. Nike became the largest sports clothing company in the world by connecting their brand to stars like Michael Jordan and Tiger Woods. And even 100 years ago, Edward Bernays was writing about similar ideas in his book Propaganda, which said: “If you can influence the leaders, either with or without their conscious cooperation, you automatically influence the group which they sway.” (Bernays is seen as the father of public relations, and his classic ideas about advertising psychology still ring true)

Read our summary of Propaganda by Edward Bernays

The third principle is Social Proof, which means when we see other people doing something, then we assume it is correct for us to do that too. This is why customer reviews, testimonials or celebrity endorsements can increase sales of a product.

5. Liking: We prefer to say yes or buy from people we like

The fourth principle of influence is Liking. This means when we feel good about someone, then we are more likely to say yes to them, buy their product, or comply with their requests.

Network marketing or multi-level marketing companies are successful because of this principle. In network marketing, people sell products from companies like Tupperware of Amway directly to their network of friends and associates. It is much easier to say no to an anonymous salesperson than your longtime friend. In fact, people are twice as likely to purchase Tupperware because they want to support their friend than because they like the product itself, according to consumer researchers Frenzer and Davis.

Customer referrals are also effective because of liking. Referrals are when a company asks a past customer whether they know anyone else who may like their products. If any names are offered, the salesperson can contact them by first mentioning the friend who gave the referral. It’s a way of piggy-backing on the existing trust between the past customer and the new prospect.

Factors that increase liking include:

  • Similarity. We like people who are like us. This is why salespeople often try to create rapport by finding any hobbies and interests they have in common with their prospect.
  • Familiarity. We tend to trust people more when we’ve seen them many times. Joe Girard was recognized as one of the world’s greatest car salesmen. He said the secret to his success was sending out greeting cards every month to 13,000 of his former customers.

    If you are building a business, you can make yourself more familiar to your prospects through a consistent email newsletter or Youtube channel.
  • The Halo Effect. One positive trait about someone can cast a halo over our whole perception of them. For example, many studies have found that physical attractiveness makes us assume someone is more intelligent.

The fourth principle is Liking. When we like someone, we want to buy from or say yes to them. Factors that increase liking include similarity, familiarity and attractiveness. Customer referrals and network marketing piggy-back off existing trust between people.

6. Authority: We follow people in positions of authority

The fifth principle is authority. This means we obey directions from people who appear to be recognized experts, leaders or officials.

When we’re kids, we follow the directions of our parents. As we grow up, we meet other authority figures like teachers, bosses and doctors. As with the other principles of influence, this usually serves us well. Parents understand the world far better than a 3 year old. Medical doctors earned their position of respect through years of learning. However, we can also be vulnerable to be tricked by false authorities.

Some common signals of authority include:

  • Clothes. We often judge someone’s position by the clothes or uniform they wear. Some medical ads take advantage of this by hiring actors who play doctors on TV shows. They are not medically trained, but they wear the white coat that subconsciously conveys medical authority. Cialdini says this is also a common tactic of con artists:

Police bunco files bulge with records of con artists whose artistry includes the quick change. In chameleon style, they adopt the hospital white, priestly black, army green, or police blue that the situation requires for maximum advantage.

  • Professional titles. In one experiment, 22 nurses in a hospital were phoned by someone claiming to be doctor, who told the nurses to give a patient some medicine. The problem was that the man was not a doctor and the dose of medication he prescribed was deadly! Yet 95% of the nurses went to follow the directions. On their way to the patient, they were stopped by another researcher who informed them of the experiment. This demonstrates the power of automatic obedience to a title.

    Certain titles are legally protected, but other official-sounding titles can be totally fabricated. When someone says they are a “Certified Nutrition Consultant,” how much training have they really done?
  • Specialization. We all assign more authority to the specialist. If you have strange feelings in your chest, would you prefer to see a General Practitioner or a Heart Specialist? If you run a small business, would you hire a general accountant or someone whose business card says “Small Business Accountant.” This one isn’t mentioned by Cialdini, but I believe it’s a powerful signal of expertise.

The marketing experts Al Ries and Jack Trout say the most important part of setting up a new business is choosing a specialization. They write, “The essence of marketing is narrowing the focus. You become stronger when you reduce the scope of your operations. You can’t stand for something if you chase after everything.” Many new entrepreneurs have a natural instinct to appeal to as many people as possible. But they say in reality, a narrow focus makes attracting customers much easier, especially as a startup.

Browse our summary of The 22 Immutable Laws of Marketing

Cialdini’s fifth principle is authority, which means we follow people who seem to be authorities. Common signals of authority include uniforms, professional titles and specialization. Specialization means having a narrow focus of expertise, like a Heart Surgeon.

7. Scarcity: We want things more when they’re harder to get

The sixth principle is scarcity, which means we value and desire things more when they appear less available. Younger people are probably familiar with the related term “Fear of missing out” or FOMO (

Daniel Kahneman is a psychologist and economist who studies how people make decisions. He found that people were 2.5 times more motivated to by a fear of losing money than they were by a desire of winning the same amount of money. This principle, which he called “The Loss Aversion Bias,” really helped quantify the effects of scarcity.

Read our summary of his book Thinking, Fast and Slow by Daniel Kahneman

Some common scarcity techniques include:

  • Limited quantity Only selling up to a certain number of a product automatically makes it more exclusive. For this reason alone, special editions usually command a higher price. For example, in one experiment by Stephen Worschel, people rated chocolate chip cookies better when they came from a jar with two cookies rather than a jar with ten cookies.
  • Limited time. Only selling a product up to a deadline. Most sales promotions use a variation of this to motivate people to come into stores.
  • Auctions. Auctions are settings of acute scarcity, with many buyers competing for one product. This is why people can become irrational in the heat of an auction, spending more money than they had planned.

The sixth principle is scarcity, which means we desire things more when they’re less available. Scarcity can be seen in auctions, and when products sold for a limited time or in a limited number.


Congratulations! Whether you just learned Cialdini’s principles for the first time or you were refreshing your knowledge, this is timeless knowledge. It provides a solid foundation for better understanding sales, marketing and persuasion in almost every situation.

The best book to read next would be Pre-Suasion, which is like Cialdini’s sequel to Influence. That one talks about the critical importance of attention, and how our focus can be directed and misdirected by others. Definitely check it out!

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